This application claims the benefit of Japanese application no. 2001-105892, filed Apr. 4, 2001, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a photoconductor used in electrophotographic apparatuses, in particular, to an electrophotographic photoconductor and method of manufacturing thereof exhibiting excellent characteristics of residual potential and repetition potential by virtue of improved additives in a photosensitive layer and coating liquid to form the photosensitive layer.
2. Description of the Related Art
A photoconductor is required to have functions of maintaining surface charges in the dark, generating charges upon receipt of light, and transporting the generated charges upon receipt of the light. Conventional photoconductors include a so-called single-layer type photoconductor having the functions in a single photosensitive layer, and a so-called laminated-layer type photoconductor having function-separated two layers: a first layer that mainly serves to generate charges upon receipt of light and a second layer that serves to maintain surface charges in the dark and transport the generated charges upon receipt of the light.
To form images by an electrophotographic method using the above types of photoconductors, a Carlson process, for example, is applied. The image formation by this process may be performed by charging the photoconductor in the dark by a corona discharge, forming an electrostatic latent image, representing characters or drawings of an original on the charged surface of the photoconductor, developing the thus formed electrostatic latent images by means of toner particles, and transferring and fixing of the developed toner image onto a support, such as paper. After the toner image is transferred, remaining toner particles are eliminated and residual electrostatic charges are removed by erase exposure, so that the photoconductor can be used again.
As photosensitive materials of the photoconductors, there have been used inorganic photoconductive substances, such as selenium, selenium alloys, zinc oxide, and cadmium sulfide dispersed in a resin binder. Besides, organic photoconductive substances, such as poly-N-vinylcarbazole, 9,10-anthracenediole polyester, hydrazone, stylbene, butadiene, benzidine, phthalocyanine and bisazo compound have been also used by dissolving and dispersing in a resin binder, or by deposition in a vacuum or sublimation.
In order to improve performances and prevent defects of the photoconductors, studies have been made on photosensitive materials and improved techniques have been proposed on photoconductors and their manufacturing methods. Improvement of photoconductor performances is widely intended by including some additives in the photosensitive layer of a photoconductor.
It is known in a field of electrophotographic technology to use a phosphate compound as such an additive. Japanese Unexamined Patent Application Publication S53-59429, Japanese Unexamined Patent Application Publication H8-314240, and U.S. Pat. No. 5,759,727 disclose a use of a triphenyl phosphate as a plasticizer to obtain flexibility or a material to attain transparency. Japanese Unexamined Patent Application Publication H8-297373 discloses a use of triphenyl phosphate in order to obtain an electrophotographic photoconductor that hardly accumulates residual potential in repeated operations under a high temperature and humidity environment and exhibits excellent durability.
Although numerous studies have been made on electrophotographic photoconductors and their manufacturing methods as described above, fully satisfactory performance has not been attained yet. In particular, the characteristics of residual potential and repetition potential need further improvement.
To solve the above problems, an objective of the present invention is to provide an electrophotographic photoconductor that exhibits excellent characteristics of residual potential and repetition potential by using a compound as an additive that has never been used in a photoconductor. It is another object of the invention to provide a method for manufacturing such a photoconductor.
The inventors of the present invention have made intense studies to solve the above problem and found that both residual potential and repetition potential substantially decrease when tri(4-nitrophenyl) phosphate is contained as an additive in a photosensitive layer of the photoconductor. The invention has been accomplished based on the aforementioned finding. Although conventional techniques to use a phosphate compound, such as triphenyl phosphate as an additive have been known, the conventional techniques do not include using tri(4-nitrophenyl) phosphate at all, which indicates that an effect of the tri(4-nitrophenyl) phosphate on photoconductor characteristics is unclear. The inventors gave attention to the tri(4-nitrophenyl) phosphate and clarified a relationship between the phosphate compound and photoconductor characteristics. Thus, a photoconductor having satisfactory performance has been obtained and a manufacturing method for such photoconductor has been established.
A photoconductor of the present invention includes a conductive substrate and a photosensitive layer on the substrate, the photosensitive layer including tri(4-nitrophenyl) phosphate. A method of the present invention to manufacture a photoconductor includes forming a photosensitive layer by coating a conductive substrate with coating liquid including photosensitive material and tri(4-nitrophenyl) phosphate.
These together with other objects and advantages, which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.